Echo ranging system



Sept. 23, 1952 w. F. MEEKER ETAL ECHO RANGING SYSTEM Filed Jan. 29, .1948

INVENTORS WILLARD F. MEEKER y FRANK H. SLAYMAKER ATTORN Y fiatenteci Sept. 2 3, i952 JUNITED STATE ranging-system, and "more particularly to an arrangement -for substantially -eliminating spurious-responses-in such a lsystem. Although not limited thereto... it is especially applicable-tosysterns; utilizing ultrasonic energy.

@In. an echo ranging system of the latter type, it gis [common practice to employ a transducer unit comprising a radiator, as for example a loudespeaker, and a weceiver or microphone placed-side byaside "In operation, .a pulse of ultrasonic energy '91 sound is emitted by i the radiator-and, if the sound strikes an object, -a portionofit is echoed or reflected and picked up :bythe microphone. Jlhelength of time elapsing between emission and reception;of-the-pulse is theme-measure otthedistance betweenthe trans- 'ducer.1;un; t -:-and the object. The radiator and the ;microphone 1 each has its response -conrined principally to a rather narrow 'beamso thatwhen they-are p c d side by side and aligned with -their-axes :of "maximum response substantially parallel, the direction in which theobjecttis located'rrnay be determined bymo-ving'the transducer unit until the maximummeturningecho is received. 1

echo rangingfsystems oftheabove outlined Lconventional .type inwhich thetransducers are located-side by: sidea portion of the outgoing *10 claims. (013181- 03) pulse .of ultrasonic energy is d ifiracted. at the edges- 9f the radiator and :tIlQ- mlOIODhOHQ, and thus :is itransmittedrdirectlyfrom; the radiator toitheamicrophone withoutbeing echoedor re- .flectediromadistant object. The result of such diffraction is a spurious; response which is indis- Ttinguishable from the response which would be obtained due to energy echoed or reflected" from a smallobject ver-y'close tothe' transducer It. is-a principal. object ofthe present inveni, "on, therefore. to ;.provlde "an "improved echo rangingl system in which'spiiriou's responses are substantially eliminated.

Titfisla further. bbjject of the presenrinvention substantially to eliminate spurious responsesby providing a pluralitybf diffraotion pathsin' an echoranging system; the relative lengths of the j'p'aths being such that the energy difiracted i oug'h one. of ltheyp'aths' is effectively canceled. by energy diffracted through one'orimore or the remaining. paths. H

' I"'1n;acc'ordancewitn thefinventiony' there is .brviddfln anlcho ranging system; a pair or transdueerswhicn aredisposed in close proximity fiitlil their. axes" of maximum 're'sp'onse'substantia1ly'parallel. one oi."theitransducersprovides v 9; beamed radiation 'adaptedto be 'echoed or re- 1.2 fiected byla distantobje'ct; and the secomtransducer. is adapted toflbe energized by. the reflected radiation. Means are provided for .aminimizing the effect. upon the second. transducer. of energy transferred ,due to Tdiiiraction from "the .jfirst transducer. .These .means comprise {first second .di'firaction paths between =.the1transducer's, the effective lengthof one of the pathsexceedingnthe ellectivelength .of the other...path by an-i oddnumber or. half wavelengths o filthe radiation. .For. example, there maybe provided-a barrier I disposed substantially perpendicularly tothe Pplane including the axes of the transducers andext'ending across-only a portion of thedifira'ction path7between the transducers. i'I'he axial length of thebarrier. is such that the. energy directly difiracted 1 between the transducers 1 is substantially canceled by theene'r'gy 'clifil iactd around the barrier. Morespecifically, theaxial length of the barrier may b'eisucl'i' that'the diffractionp'ath around'the barrier is 'anf 'odd' number of half wavelengths of the beamedira'di'ation longer than-the direct'di'ffraction path. [The edge or the barrier'remotefromthe transducersmay besub'stantially parallel to the planeof theppe'ning's' thereof, or it "maybe *disposed at anall- .propr'iate' "angle'with respect thereto.

"The "invention "will b'e better understoodwy r'e'ference'- to the "following description" taken in "conjunction j with (the drawing, "in -which like component's aredesignated bylike reference no;- merals and in which;

"Figf l" is a-perspective view of that portion'pi' an echotranging system incorporatihg'the f im- "provements of the present invention; and

Figs. 2 and *3- are respectivel'y modified embodiments' of the' arrangement of Fig. 1. 7

Referring "to Fig. 1 g' of the -drawing,* there--'is shown apair of transducers land 2,=transducer I comprising aradiator or'loud speakec adapted i emit ultrasonic energy or sound which -"is diagrammatically represented byarrows 3. Transduce'r 2, which may t for examplecomprise a microphone, is -adaptedto receive ultrasonic "energy -refleeted from a distant object *(not shown) I the reflected energy being diagram-- "maticallyindicated-by arrows 4. The transducers may poz' respond to those shovvn and claimed-in Patent 2,541,944; issued February 13;- 1951; to F. H. Slaymaker et al., and assigned-tothe same assignee the' present invention Whereinithe directions of maximum response are a substan- By virtue of the above-described relative arrangement and proportions of barrier 6, the ultrasonic energy following the direct diifraction path 5 from transducer I to transducer 2 will be substantially canceled by ultrasonic energy following the diffraction path 8 around the end of barrier 6, so that there will be no appreciable response from transducer 2 due to diffracted sound energy. The presence of barrier 6, however, has no appreciable effect upon the transfer'of'energy from transducer I to transducer 2 over the reflection paths 3' and 4.

' Although the outer edge I of barrier 6- is shown substantially parallel to the planes of the openings of transducers I and 2, it will be understood that the angle of edge 1 may be adjusted to secure an even closer agreement between the magnitudes of directly diffracted ultrasonic energy and of the ultrasonic energy diffracted around, barrier 6. These two magnitudes are preferably made closely equal by proper choice of the vertical dimension of barrier 6, a final exact balance then being secured by a slight adjustmentof the position of barrier 6 with respect to transducers I and 2. Barrier 6 may be of any suitable material, as for example cardboard or metal.

IFig. 2 shows a modification of the present invention in which, instead of employing a separate barrier as shown in Fig. 1', a slot is provided between the transducers to secure first and second diffraction paths of different lengths. In the arrangement of this figure, transducers I and 2 are. positioned closely adjacent each other with' their axes of maximum response substantially parallel. A slot 9 is cut in the adjacent portions of the two transducers, the depth of this slot and its transverse length being such that the energy diffracted through the slot is of the proper phase and magnitude substantially to cancel the energy diffracted directly between the transducers.

Still another modification is shown in Fig. 3,

.in which transducers I and 2 are disposed as in Figs. 1 and 2. A rod-like obstacle I0 is provided,

, and it is disposed substantially perpendicularly ,to the plane including the axes of maximum response of the transducers. This obstacle serves to scatter aportion of the diffracted energy from .one of the transducers, and thus modifies the magnitude and of proper phase effectively to cancel the energy difiracted directly between the transducers. I

. In order to secure the maximum benefit from the arrangements in accordance with the present invention, it is necessary to minimize other forms of coupling betweenthe transducers. Electromagnetic and electrostatic coupling may be .-.satisfactorily minimized by the use oftwo-coniwithj pairijof directional transducers facing in the same direction and disposed in. close proximity ductor shieldedcables to the transducers, with the shield grounded to the covers and to the frame connecting the transducers. Mechanical transmission through the frame joining the transducers may be reduced to a, satisfactory value by the use of resilient grommets to isolate each transducer from the connecting frame. Any direct transmission between' transducers may be minimized by suitable acoustic treatment of the rear cover of each transducer, and by providing suitable acoustic seals for any small openings in the housings thereof.

In one particular embodiment of the present invention in accordance with Fig. l, in which the radiated ultrasonic energy had a frequency of 65 kilocycles per second, a 10:1 reduction in the response due to diifracted energy was readily secured, using transducers having a radius of ducers" are used for'transmi'ssion and reception,

the arrangements of the present invention are suitable for substantially eliminating spurious responses due to diffraction at the adjacent edges of the transducers; a

While there has been-described wh'z'it is at present considered the preferred embodiment of the invention, it will be obvious to thoseskilled in the art that variouschanges and modifications may be'rnade therein without departing from; the invention, and it is, therefore, aimed in-theap pended claims to cover all such changes odifications as fall within the true spirit-and scope of the invention.

What is claimed is:

1. In an echo ranging systerh,in combination with a pair of directional transducers facing in the same direction and disposed in close proximity with their axes of maximum" response substantially parallel, one of said transducers providing a beamed radiation adapted tobe refiected by a distant objectand the second trans ducer being adapted to be energized by said reflected radiation, the beamed radiationbelng subject to diffraction whereby a spurious-re- 'sponse may be produced by said second-transducer, andmeans for minimizing the effect-upon said second transducer of energy transferf'due to said diffraction from said first transducer comprising a barrier disposed betweensaidtransducers substantially perpendicularly to theplane including said axes and parallel to said axes and extending across only a portion of-the diffraction path between said transducers, ;th'e ":axial length of said barrier being. such that the energy directly diffracted between saidtransducersis substantially' canceled by the, energy .idiflracted around said barrier. 3

2. In an. echo ranging system, inrcombination with their-axes of maximumflresbonse substantiallyparallel, oneof said transducers providinga beamed radiation of predetermined waveenergy transfer due tosaid diffraction from said first t an du r comprisin a. barri r di p between said transducers substantiaily pen pendicularly to the .pl au e including said axes and parallel to said axes and extending across only aiportion of the diffraction path between said transducer, .the axial length of said barrier being such that the diffraction-fpath around said a barrier is odd number fofli'half wavelengths lorig'er than the direct diffraction path, whereby the energy directlydiifract'ed between said transducers is s'ubstantially canceled by the energ diifracted around said barrier.

3. In an echo ranging system, in combination with a pair of directional transducers facing in the same direction and disposed in close proximity with their axes of maximum response substantially parallel, one of said transducers providing a beamed radiation adapted to be reflected by a distant object and the second transducer being adapted to be energized by said reflected radiation, the beamed radiation being subject to diffraction whereby a spurious response may be produced by said second transducer, and means for minimizing the eifect upon said second transducer of energy transfer due to said diffraction from said first transducer comprising a barrier disposed between said transducers substantially perpendicularly to the plane including said axes and parallel to said axes and extending across only a portion of the diifraction path between said transducers, the angle between the plane of the openings of said transducers and the edge of said barrier remote from said transducers being so chosen and the axial length of said barrier being such that the energy directly diffracted between said transducers is substantially canceled by the energy diffracted around said barrier.

4. In an echo ranging system, in combination with a pair of directional transducers facing in the same direction and disposed in close proximity with their axes of maximum response substantially parallel, one of said transducers providing a beamed radiation adapted to be reflected by a distant, object and the second transducer being adapted to be energized by said reflected radiation, the beamed radiation being subject to diifraction whereby a spurious response may be produced by said second transducer and means for minimizing the effect upon said second transducer of energy transfer due to said diffraction from said first transducer comprising a barrier disposed between said transducers substantially perpendicularly to the plane including said axes and parallel to said axes and extending across only a portion of the diffraction path between said transducers, the edge of said barrier remote from said transducers being substantially parallel to the plane of the openings thereof and the axial length of said barrier being such that the energy directly diifracted between said transducers is substantially canceled by the energy diffracted around said barrier.

5. In an echo ranging system, in combination with a pair of directional transducers facing in the same direction and disposed in close proximity with their axes of maximum response substantially jparallel, "one of said transducers are: viding a" beamed radiation of predetermined wavelength adapted to :be reflected :by a distant object and the second transducer :beingadapted to be energized'bysaid reflected radiation, the beamed radiation being subject to diffraction whereby a spurious response may be produced by "said second transducer, and means forwminimizing the eiiectupon said second transducer of energy transfer due to said diffraction from said first transducer; comprising. a barrier disposed between "said transducers substantially perpendicularly, to the plane including said axes-:and parallel to said axes and extendingacross only a portion 'ofz'the diffraction path betweeneisaid transducers, theed'ge-of said barrierzremote from said' transducers being substantially parallelto the fplane thereof and the axial lengthiof z said barrier being such that the diffraction :path' around said barrier is an odd number of half wavelengths longer than the direct difliraction path, whereby the energy directly diffracted between said tranducers is substantially canceled by the energy diffracted around said barrier.

6. In combination, a directional acoustical radiator and a directional microphone disposed in close proximity with their axes of maximum response substantially parallel and their openings faced in the same direction, said radiator and said microphone being of substantially equal radius, and a barrier of sheet-like material disposed between said radiator and said microphone substantially perpendicularly to the plane including said axes and parallel to said axes, said barrier extending in an axial direction beyond said radiator and said microphone openings a distance forming a substantial portion of a multiple of a quarter-wave length in the frequency of operation of said acoustic radiator, and extending in a transverse direction from said plane a distance substantially equal to said radius.

7. In an echo ranging system, in combination with a pair of transducers disposed in close proximity with their axes of maximum response substantially parallel, one of said transducers providing a beamed radiation adapted to be reflected by a distant object and the second transducer being adapted to be energized by said reflected radiation, means for minimizing the effect upon said second transducer of energy transfer due to diffraction from said first transducer com prising a slot in the adjacent'portions of said transducers, the dimensions of said slot being such that the energy directly diffracted between said transducers is substantially canceled by the energy difiracted through said slot.

8. In an echo ranging system, in combination with a pair of transducers disposed in close proximity with their axes of maximum response substantially parallel, one of said transducers providing a beamed radiation adapted to be reflected by a distant object and the second transducer being adapted to be energized by said reflected radiation, means for minimizing the effect upon said second transducer of energy transfer due to diffraction from said first transducer comprising a rod-like obstacle disposed substantially perpendicularly to the plane including said axes, the displacement of said obstacle from said transducers being such that the energy directly diffracted between said transducers is substantially canceled by the energy difiracted to and scattered by said obstacle.

9. In combination, an acoustical radiator and a microphone disposed in close proximity with direction, said radiator and said microphone being of substantially equal radius, and a rod-like obstacle disposed substantially perpendicularly to the plane including said axes, the displacement of said obstacle from saidlradiator and said parallel and; their openings 'faced'in the same microphone beingisuchkthat the" nergy direetlyt diffractedbetween said radiator and-said micro-i phone is substantially-canceled by. .thezenergy diffractedto: and scattered by saido'bstacle;

'.FRANK H, SLAYMAKERJ:

file of this-"patentr I V w v UN T WAW F' E SEI- Number The following references are or record" in 'tl'i 7 Name l p 2,103,357 W Gerhard Dec. 28; 1937 v2,177,769 Erickson .0ct. 31, 1939 2,208,160 McCreary July: 16, 1940 2,270,965, 7 Peterson in; Jan. 27,21 942 2,287,533 Peterson- :June 23,1942 2,455,888 Brown v Dec. 751 948 pate 

